SATURN (MYTHOLOGY)
An ancient Roman god of agriculture, Saturn was later
identified with the Greek god CRONUS, who fled to Italy after
his dethronement by Zeus as ruler of the universe. Saturn
settled on Rome's CAPITOLINE HILL and taught the people
agriculture and other arts of civilization. He helped usher in a
period of prosperity that became known as the Golden Age.
One day Saturn vanished from the earth. At the Saturnalia
festival, held in his memory every December (the winter sowing
season), masters and slaves shared the same table as a sign
that no social divisions existed during the Golden Age. Saturn
also gave his name to a planet and to Saturday.
Saturn
Divorcee
wearing 7 rings from 7 failed marriages
conceiving 18 children
yet still cosmetically adorned
in wait for whichever husband may happen to return
daring the bachelor to come along
and experience this bride and her pregnancies
before her insatiable loneliness
with its responsibilities
forces him to move on.
carlyle miller

Saturn

Saturn: Mimas

Saturn: Moons

Saturn: Mimas

Saturn: Dionne

Saturn: Enceladus

Saturn: Hubble pic

Saturn: Rings

Saturn: Rings

Saturn: Small Satellites

Saturn: Ethys

SATURN (PLANET)
Even when viewed through a small telescope, Saturn and its ring
system is one of the most unique objects in the sky. With a
large modern telescope in good observing conditions, the planet
appears as a light yellow and gray banded oblate spheroid.
Like the other giant planets--Jupiter, Uranus, and Neptune--the
visible planet is the cloud top of an extensive gaseous
atmosphere.
THE PLANET
Saturn orbits the Sun at a mean distance of 1.427 billion km
(0.893 billion mi) with a period of 29.4577 tropical years.
The orbit is inclined 2.49 degrees to the ecliptic, or
Earth-orbital, plane and has an eccentricity of 0.0556. At
Saturn's distance from the Sun, it receives only 0.01 of the
unit solar radiation flux that the Earth does. Among planets
in the SOLAR SYSTEM, Saturn is second in size only to Jupiter;
Saturn has an equatorial diameter of 120,660 km (74,980 mi).
Its volume would enclose about 769 Earth-sized bodies.
Saturn's internal rotation period, defined by periodic radio
emissions, is 10.657 hours. This fast rotation is responsible
for Saturn's equatorial bulge and oblate shape. The
equatorial-polar-diameter ratio is 1.12 to 1. Saturn's mass is
5.686 X 10 to the power of 26 kg (12.54 X 10 to the power of 26
lb), or 95.147 times the Earth's. Thus the average density is
only 0.69 g/cu cm (43 lb/cu ft), which is much less than water,
indicating a very deep atmosphere and a very small core.
Atmosphere
Saturn is one of the giant outer planets, which are
characterized by their large size, low density, and
corresponding extensive atmospheres. Current models of the
interior indicate that below the relatively thin opaque cloud
layer is an extensive, clear hydrogen-helium atmosphere. Data
on the internal heat flux, the detailed gravity field, and the
observed upper-atmosphere hydrogen-helium ratio satisfy a model
of the interior where the ratio of hydrogen to helium decreases
with depth. The gas density gradually increases downward and
the gas transforms into a liquid. Further down the pressures
increase to a critical level, and there the hydrogen becomes
metallic. A small core of silicate material probably exists at
the center.
The Saturnian atmosphere is characterized by counterflowing
easterly and westerly jet streams that, at the equator, reach a
speed of 480 m/sec (1,070 mph) relative to the clouds at 40
degrees latitude. The zonal jets do not change appreciably
with time, but smaller-scale spots, waves, and eddies were seen
on VOYAGER spacecraft images to change a time scale of hours.
Such smaller features are usually hard to observe on Saturn
because of an obscuring haze layer above the planet's cloud
surface. One northern hemisphere feature, however, known as
the Great White Spot, does become significantly noticeable for
Earth-based viewers about every 29 years. The spot is
apparently an upwelling of ammonia-rich materials; the ammonia
then crystallizes at this greater height to produce the white
color. The spot sometimes expands until it becomes a band of
clouds girdling the planet.
Traces of methane, ethane, phosphine, and acetylene also exist
in the hydrogen-helium atmosphere. Various colors that have
been observed probably result from chromophores being produced
by the interaction of such trace elements as sulfur or carbon
compounds with ionospheric charged particles and lightning.
This condition of chemical nonequilibrium is produced by
vertical mixing, driven by heat from the gravitational energy
released by the precipitation of liquid helium. Saturn
radiates 2 to 3 times the heat absorbed from the Sun.
Magnetic Field
Saturn has a strong, dipolar magnetic field tilted only 0.7
degrees from the rotational axis. The subsolar magnetopause is
6.38 million km (3.96 million mi) from Saturn on the average.
A magnetic tail extends in the direction away from the Sun much
like cometary plasma tails. Saturn's magnetic field traps
charged particles coming from the solar wind. These particles
move along magnetic-field lines but are absorbed by satellites
and ring particles. The charged particles that impinge on the
ionosphere create airglow emissions.
Origin and Evolution
Saturn is far enough away from the Sun to retain the light
elements (hydrogen and helium) and therefore has solarlike
chemical abundance. Saturn's mass, unlike that of the Sun, was
not large enough to initiate the fusion process, and Saturn,
unlike Jupiter, did not give off enough excessive heat to drive
out water from the inner satellites.
THE RINGS
Saturn's white rings were first seen by Galileo Galilei in
1610; his small, imperfect telescope showed the planetary disk
flanked by what he first interpreted as being two smaller
bodies. Christiaan HUYGENS correctly theorized (late 1650s)
the ring nature of these alleged "companions." James Clerk
MAXWELL mathematically demonstrated (1857) that the rings were
composed of many small, unconnected particles, each orbiting
near Saturn's equatorial plane.
The classical designations for the rings are based on the gross
ring components identified from the ground, but the Voyager
spacecraft have shown the ring system to be highly structured.
The radial particle-density distribution changes over distances
of hundreds of meters, but individual particles, whose
estimated sizes range from tens to hundreds of centimeters,
have not been resolved. The ring plane has a maximum thickness
of 1 to 2 km (0.6 to 1.2 mi). Spectroscopy shows the presence
of water ice, which probably covers rocky silicate cores.
The dynamics of the rings are not presently well understood.
The theory of satellite resonances predicts that particles
whose orbital periods are integral fractions (such as 1/2 or
2/3) of the periods of the satellites become either locked into
or perturbed out of a particular orbit, but only a few of the
observed gaps can be explained in this manner. Voyager showed
eccentric ringlets and asymmetrical kinks in some ringlets.
The kinks in the F ring gave it a braided appearance, but
despite the proximity of two small satellites, the kinks do not
seem directly related to them. Voyager also showed irregular
spokelike features in the B ring that are composed of very
small, strongly back-scattering particles temporarily out of
the ring plane. Because of the detection of electrostatic
discharges from the rings at radio wavelengths, these particles
are thought to be electrically charged and thus forced out of
the ring plane by Saturn's magnetic field.
The rings may be the debris from satellites or comets broken
apart by tidal forces (see ROCHE'S LIMIT). Another hypothesis
is that Saturn's tidal forces and the perturbations of various
satellites prevented the material left over from the formation
of Saturn to accrete into further satellites.
SATELLITES
Saturn has the most extensive satellite system in the
solar system. Not counting the myriad ring particles, more
than 20 bodies orbiting around Saturn have so far been
identified. Six can be easily seen through the telescope.
TITAN is the largest Saturnian satellite and, among all
solar-system satellites, is second in size only to the Jovian
satellite Ganymede. It is the only satellite with a
substantial atmosphere, although Neptune's TRITON has a much
thinner one. The highest-resolution Voyager images show
several haze layers that together obscure the surface. (For a
discussion of this major satellite, see the article of that
name.)
The other satellites of Saturn tend to have low densities (1 to
1.5 g/cu cm, or 62 to 94 lb/cu ft) and high albedos, or surface
reflectivities (0.4), indicative of water-ice-dominated bodies.
Water frost has been detected spectroscopically on the surface
of most of these satellites. With the exception of Phoebe,
Iapetus, and Hyperion, they are in nearly circular, direct,
low-inclination orbits. All of these satellites, with the
exception of Enceladus, have highly cratered, old surfaces.
The larger satellites have two distinct crater populations,
perhaps a result of different sources and types of impacting
bodies or of changes in the impact behavior of the satellite
surfaces as they evolved.
Mimas is dominated by a crater 130 km (81 mi) in diameter, or
one-third of its own diameter. The impact that produced such a
large crater on Mimas, weakly bound by its own gravity, was
near the limit of major disruption. The remaining surface is
heavily cratered and has some grooves that may have been either
formed when the large crater was formed or developed by tidal
interactions when Mimas was still warm from accretion. Using
density measurements gathered by the Voyager 1 spacecraft,
scientists have found that Mimas may have a small rocky core
with a thick mantle of water ice.
Enceladus is unusually smooth and free of craters. Its albedo
is possibly the highest in the solar system, the result of a
substantially resurfaced ice crust. Because the orbits of
Dione and Enceladus are in resonance, the latter has an
eccentricity forced by Dione. This produces strong tides and
tidal heating, which may have kept the ice in a more fluid
state during the postaccretion impact phase. The smoother
regions have groove and ridge terrain that is very similar to
regions on the icy Jovian satellite Ganymede.
Tethys is heavily cratered and has an approximately
1,000-km-long (620-mi) valley running roughly north-south. The
terraced walls of the valley suggest crustal layering. With a
bulk density of 1.0 g/cu cm (62 lb/cu ft), Tethys is mostly
water ice. It was subject to great expansion forces upon
freezing that might have been responsible for the valley.
Dione is about the same size as Tethys but has a higher
density. High-albedo streaks or wisps on the dark trailing
hemisphere may be frost deposits produced by water escaping
from the interior through linear fractures. The crater density
is generally lower than on Mimas. Like Tethys, Dione shows
leading- and trailing-hemisphere asymmetries in albedos,
probably caused by "gardening" effects due to the sweeping up
of postaccretion-phase debris.
Rhea also shows large albedo variations and has wispy markings
like those seen on Dione. Differences in the size-frequency
distribution of craters in bright and dark terrains indicate
that the darker terrain is older. Hyperion is relatively
small, irregular in shape, and heavily cratered. The long axis
is not oriented toward the planet as would be expected in the
dynamically stable case. Iapetus's albedo varies from 0.1 to
0.5 for the leading and trailing hemispheres respectively. The
dark hemisphere is quite red, similar to the Jovian satellite
Callisto. The dark leading hemisphere may be the result of
selective impacts by carbonaceous chondritic material, but the
albedo boundary is inexplicably sharp. Phoebe is in an
eccentric, retrograde orbit expected of a body captured by the
Saturn system rather than being formed there. It is a
very-low-albedo, irregular-shaped body much like C-type
asteroids.
The coorbital satellites Epimetheus and Janus and 1980S3,
occupy essentially the same orbit between Mimas and the F ring.
Their orbital radii differ by less than their diameters, but
collisions are prevented by their mutual gravitational
interaction. These satellites, like all of the small ones, are
both irregular in shape and cratered. They were perhaps once
one body that was torn apart by a large impact. The satellite
temporarily designated 1980S28 orbits just outside the A ring
and acts as a gravitational barrier that defines the outer edge
of that ring. The satellites 1980S27 and 1980S26 orbit just
inside and outside of the F ring and probably confine the
particles in that ring. These two "shepherding" satellites
control the F ring. Telesto and Calypso are in orbits with
periods nearly the same as that of Tethys; they are located
near the stable LAGRANGIAN POINTS 60 degrees ahead (L4) and 60
degrees behind (L5) Tethys in its orbit. The satellite 1980S6
(Dione B) librates (oscillates) about the Dione L4 point and
has an irregular shape.
Bibliography: Briggs, Geoffrey, and Taylor, Fredric, The
Cambridge Photographic Atlas of the Planets (1982; repr.
1986); Gehrels, Tom, and Matthews, Mildred S., eds., Saturn
(1984); Hunt, Garry, and Moore, Patrick, Saturn (1982);
Morison, David, Voyages to Saturn (1982); Nichols, R. G.,
"Voyages to the Worlds of Ice," Astronomy, December 1990;
O'Meara, S. J., "Saturn's Great White Spot Spectacular," Sky &
Telescope, February 1991; Soderblum, L. A., and Johnson, T.
V., "The Moons of Saturn," Scientific American, January 1982;
Washburn, Mark, Distant Encounters: The Exploration of Jupiter
and Saturn (1983).[36;40;1m
RINGS AND ESTABLISHED SATELLITES OF SATURN*
---------------------------------------------------------------
Year of
Name Discoverer Discovery
-------------------------------------------------------------- D
ring inner edge
C ring inner edge
B ring inner edge
B ring outer edge
A ring inner edge
Encke division
A ring outer edge
Atlas Voyager 1 1980
Prometheus Voyager 1 1980
F ring Pioneer 11 1979
Pandora Voyager 1 1980
Epimetheus D. Cruikshank 1980
Janus D. Pascu 1980
G ring
Mimas William Hershel 1789
E ring inner edge
E ring maximum
Enceladus William Hershel 1789
Telesto Note 1 1980
Tethys Giovanni Cassini 1684
Calypso Note 2 1980
E ring outer edge
Electra P. Laques, J. Lecacheaux 1980
Dione Giovanni Cassini 1684
Rhea Giovanni Cassini 1672
Titan Christiaan Huygens 1655
Hyperion W. Bond, W. Lassell 1848
Iapetus Giovanni Cassini 1671
Phoebe William Pickering 1898
--------------------------------------------------------------- *
Several other satellites are definitely known to exist,
bringing the total number up to 24, and others are suspected.
Little is known about these tiny moons, none more than about 18
km (11 mi) in diameter. One, identified in 1990 and named Pan
in 1991, lies in Encke's division (1981S13). Three orbit
between the outer edge of the E ring and Electra (1980S34,
1981S10, and 1981S11), and three orbit between the orbits of
Dione and Rhea (1981S7, 1981S8, and 1981S9). Note 1--B.
Smith, H. Reitsema, S. Larson, J. Fountain. Note 2--Space
Telescope Wide Field/Planetary Camera Instrument Definition
Team.